(NBC News) A group of Colorado nuns don't have any reason to appeal the birth control mandate in the health care law because they don't have to provide contraception anyway, the U.S. government argued on Friday.

It's an early skirmish in a year expected to be full of battles over the so-called contraceptive mandate in the Obamacare law.

The administration says the group is already exempt from the law, because their insurance is provided by Christian Brothers Services. As a church organization, it's excused from the law's requirements. The nuns have said they don't want to sign a waiver asking for an exemption.

"They need only self-certify that they are non-profit organizations that hold themselves out as religious and have religious objections to providing coverage for contraceptive services," the Department of Justice wrote in its response.